Omar Suleiman, Mubarak's intelligence chief and vice-president during the final days of his presidency, registered less than half an hour before the 2pm local time (1200 GMT) deadline.

"The people want Omar Suleiman," his supporters chanted as he struggled to get through the crowds outside the election commission.

Politician Ayman Nour, whose unprecedented challenge to Mubarak in presidential elections in 2005 earned him worldwide recognition, was disqualified by a court on Saturday from contesting because of a conviction for alleged fraud.

The country's ruling military council had earlier agreed to let him run. Nour's lawyer said he would be appealing the latest ruling, the official Mena news agency reported. Saturday's verdict said he could only stand for the presidency six years after his pardon.

Bothaina Kamel, the only woman to announce a bid, failed to gather the required 30,000 voter signatures to qualify but she told reporters she would "continue to work to develop the political conscience of the Egyptian people".

The Supreme Council of the Armed Forces [SCAF], which took power after Mubarak was toppled, has said it will hand power to civilian rule in June after a president is elected.

Registration drama

Fearful that their primary nominee could also be disqualified, the Muslim Brotherhood, the country's most influential political group, nominated the head of its party as a back-up candidate.

In a statement released late on Saturday, the Brotherhood said they were putting forth party leader Mohammed Morsi as an alternate to Khairat el-Shater, the party's chief strategist and financier.

The group fears Shater could be banned under the same rule as Nour, as he was released from prison last month after serving five years on charges of being a member of the then-outlawed Brotherhood.

The Brotherhood, which won nearly half the seats in parliament in recent elections, said in its statement that there appeared to be efforts by Egypt's election committee to disqualify certain candidates from the race.

"There are attempts to create barriers for some candidates," the group said, adding some sections wanted the former regime to return to power.

"Because we are protecting the success of the revolution and all of its goals ... we have decided as the Brotherhood and its party to nominate Mohammed Morsi as our back-up candidate for president," the statement said.

Shater's nomination had marked a political U-turn for the Brotherhood, which had earlier vowed not to field a candidate.

The Brotherhood announcement came hours after the ultra-conservative Gamaa Islamiya put forward a religious leader as its back-up candidate after reports surfaced that the group's first choice, Hazem Abu Ismail, could also be disqualified with the election commission saying his mother was a US citizen.

Egypt's election rules state that both parents of presidential candidates must be Egyptian nationals.

Gamaa Islamiya said it selected Safwat Hegazy, a prominent imam who preaches on television, as a back-up to Abu Ismail.

The first round of the election is due to take place on May 23 and 24.